Answer: Small box = $5
Large box = $14
Explanation:
Let the cost of a small box be a
Let the cost of a large box be b
The scenario in the question can be modelled into an equation as:
3a + b = 29 ....... equation i
3a + 4b = 71 ....... equation ii
Subtract equation ii from equation I
-3b = -42
b = 42/3
b = 14
Cost of large box = $14
We put the value of b into equation I
3a + b = $29
3a + $14 = $29
3a = $29 - $14
3a = $15
a = $15/3
a = $5
Cost of small box = $5